Microstructure of Bioglass/Hydroxynpatite Coatings on Ti Substrate

Composite coatings of bioglass and hydroxyapatite (briefly named HA/BG) with different hydroxyapatite contents on titanium substrate were successfully fabricated. The fabricated coatings are characterized by rough and poriform surface.The densities of the coatings decrease with the increase of HA content. There is a transition layer with a 5 μm thickness between the BG coating and the substrate. During heat-treatment, hydroxyapatite crystals with hexastyle shape have precipitated from the BG.     

Morphology and immersion behavior of plasma-sprayed hydroxyapatite/bioactive glass coatings

A series of hydroxyapatite/bioactive glass (HA/BG) coatings have been plasma-sprayed on Ti6Al-4V substrate using HA/BG powders that were prepared by both sinter-granulation and direct mixing methods. The morphology and immersion behavior of these coatings in a simulated body fluid (SBF) were investigated. The results showed that in-house fabricated BG and sinter-granulated HA powders were irregularly shaped and dense. When 5 wt % or more BG was added in HA, the powder became rough and porous. X-ray diffraction (XRD) patterns showed that the presence of BG enhanced the decomposition of HA structure during fabrication of the powders. Reasonably high bond strengths were obtained from all coatings. The granulated type HA/BG coatings showed no significant differences in bond strength from the mixed type HA/BG coatings. The plasma spray process itself and the presence of BG enhanced the decomposition of apatite. Surface morphology of all sinter-granulated type coatings was similar to that of monolithic HA coating, that was comprised of patches of smooth and shiny glassy film and irregularly-shaped particles on its surface. The dissolution depth of plasma-sprayed coatings immersed in SBF was largely dependent on the type and composition of the coating. Granulated type HA/BG coatings were much less dissolvable than monolithic HA or mixed type HA/BG coatings. It seems that the presently used granulation method for the preparation of HA/BG powders plays a predominant role in determining the dissolution behavior of the plasma-sprayed coatings. ©©2000 Kluwer Academic Publishers     

纯钛表面HA/BG生物复合涂层的组织结构研究

通过高温熔烧法在工业纯钛ＴＡ３表面制备出不同羟基磷灰石含量的羟基磷灰石与生物玻璃的复合涂层（简称ＨＡ／ＢＧ）,对复合涂层的微观组织结构进行了研究,结果表明,所制生物玻璃的高温处理的过程中会析出六方柱状的ＨＡ晶体,复合涂层具有粗糙表面,存在很多开放性气孔,随着ＨＡ原始含量的增加,复合涂层的致密度明显降低,而复合涂 ＨＡ相的衍射峰强度变化不大。     

Ti-6Al-4V合金基体等离子喷涂生物活性羟基磷灰涂层的研究进展

系统阐述了在钛合金(Ti-6Al-4V)表面等离子喷涂羟基磷灰石(HA)涂层的研究进展.描述了等离子喷涂制备HA涂层的工艺过程、微观形貌和化学组成.综述几种综合性能较高的复合型涂层:HA/BG(生物活性玻璃)复合涂层,HA/ZrO2复合增强型涂层,HA/Ti涂层,HA/Ti-6Al-4V梯度涂层;并对HA涂层发展趋势进行了展望.     

Structure and properties of hydroxyapatite-bioactive glass composites plasma sprayed on Ti6Al4V

Hydroxyapatite (HA)-coated Ti6Al4V has recently been used as a bone substitute in orthopaedic and dental applications because of its favourable bioactivity and mechanical properties. Studies in the literature have shown that the bioactivity of calcium phosphate bioactive glass (BG) is higher than that of HA. In an attempt to increase the bioactivity of Ha-coated Ti6Al4V and enhance the bonding strength between coating and substrate, in the present study, HA/BG composites are applied onto Ti6Al4V using a plasma spraying technique. Microstructure and phase changes of the composite coating after plasma spraying are studied. The coating-substrate bonding strength is evaluated using an Instron, following the ASTM C633 method. Results indicate that the average bonding strengths of BG, HA/BG and HA coatings are 33.0±4.3, 39.1±5.0, and 52.0±11.7 MPa, respectively. Open pores with sizes up to 50 m are found in both BG and HA/BG coatings, which are probably advantageous in including mechanical interlocking with the surrounding bone structure, once implanted. These HA/BG composites could provide a coating system with sufficient bonding strength, higher bioactivity, and a significant reduction in cost in raw materials. The future of this HA/BG composite coating system seems pretty bright.     

Plasma-sprayed hydroxyapatite coating: effect of different calcium phosphate ceramics

Three kinds of calcium phosphate ceramic powders, namely commercial hydroxyapatite (CHA), self-made hydroxyapatite (SMHA) and synthesized hydroxyapatite (SHA), are employed as starting materials for plasma-sprayed coating onto a stainless steel (316L) substrate. Results show a mixture of hydroxyapatite (HA), tricalcium phosphate (TCP), and tetracalcium phosphate (TeCP) phases appearing in the CHA and SHA-derived coatings and a primary of a HA with trace contents of tricalcium phosphate phases resulting in the SMHA-derived coating. The HA appears to be the only observable crystalline phase present in the SMHA-derived coating after 7 days of incubation with a simulated body fluid (SBF); however, part of the impurities, i.e. TCP and TeCP, remain in the other coatings. No apparent microcracks can be found on the coated surfaces when SMHA and SHA are used. The poor packing density of SHA reflects its weakness in bonding strength to the substrate surface compared with that obtained using CHA and SMHA powders. The surface morphology of the coatings was found to alter significantly after a sufficient period of incubation.     

Comparison of Tantalum and Hydroxyapatite Coatings on Titanium for Applications in Load Bearing Implants

Over the years hydroxyapatite (HA) coatings have been used to improve biologic properties of Ti‐based load bearing metal implants. However, applicability of HA coated implants is subjected to physical stability of the HA phase and mechanical integrity of the coating‐substrate interface. In this study, we have compared the microstructure and in vitro cell–materials interactions of newly developed laser deposited Ta coatings and radio frequency (RF) induction plasma sprayed HA coatings on Ti substrate. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed equally excellent cellular adherence and growth on Ta and HA coatings. Quantitative assay of cell survivability on these coatings showed that the Ta coatings provide comparable initial cell attachment to that of HA coatings. Microstructural analysis of the coatings showed strong metallurgical bonding without sharp interface between the Ta coating and the Ti substrate, while the interface between HA coating and the Ti substrate was sharp. The interface microstructural features and in vitro cell–materials interactions of Ta coatings on Ti clearly demonstrate their potential to replace HA based coatings for enhanced/early biologic fixation. Other significant benefits of these dense Ta coatings include high toughness, strong bonding with the substrate, and long‐term stability of the interface.     

低温熔盐电沉积羟基磷灰石复合涂层的研究

为了提高羟基磷灰石涂层的结合强度,在AlCl3-NaCl-TiCl3低温熔盐体系中加入HA微粒,复合电沉积制备Al-Ti/HA复合涂层,并对涂层的表面形貌、结构和结合强度进行了研究.结果表明: HA微粒均匀分散在Al-Ti合金镀层中,其共沉积量随电流密度的减小和熔盐中HA浓度的增大而增强;涂层的结合强度随HA共沉积量的增大而增强,当HA的共沉积量为40.1%(质量分数)时,Al-Ti/HA复合涂层的结合强度达到28.1 MPa.     

Formation of highly oriented hydroxyapatite in hydroxyapatite/titanium composite coating by radio-frequency thermal plasma spraying

Highly oriented hydroxyapatite (HA) coatings with excellent adhesion were successfully obtained on titanium (Ti) and titanium alloy through a radio-frequency thermal plasma spraying method. The ratio of HA and Ti powders supplied into the plasma was precisely controlled by two microfeeders so as to change the composition from Ti-rich to HA-rich toward the upper layer of the formed coatings. The bond (tensile) strength of the HA/Ti composite coatings was ca. 40–50 MPa. XRD patterns showed that the topmost HA layer of the coatings had an apatite structure with (00l) preferred orientation. The degree of this orientation showed a tendency to increase with an increase in the substrate temperature during spraying.     

Surface characterization of colloidal-sol gel derived biphasic HA/FA coatings

Hydroxyapatite (HA) powders are ultrasonically dispersed in the precursor of fluoridated hydroxyapatite (FHA) or fluorapatite (FA) to form a “colloidal sol”. HA/FA biphasic coatings are prepared on Ti6Al4V substrate via dip coating, 150 °C drying and 600 °C firing. The coatings show homogenous distribution of HA particles in the FA matrix. The relative phase proportion can be tailored by the amount of HA in the colloidal sol. The surfaces of the coatings consist of two kinds of distinct domains: HA and FA, resulting in a compositionally heterogeneous surface. The biphasic coating surface becomes increasingly rougher with HA powders, from around 200 nm of pure FA to 400–600 nm in Ra of biphasic coatings. The rougher biphasic HA/FA surfaces with chemically controllable domains will favor cell attachment, apatite layer deposition and necessary dissolution in clinical applications.     

Hydroxyapatite-anatase-carbon nanotube nanocomposite coatings fabricated by electrophoretic codeposition for biomedical applications

In order to eliminate micro-cracks in the monolithic hydroxyapatite (HA) and composite hydroxyapatite/carbon nanotube (HA/CNT) coatings, novel HA/TiO₂/CNT nanocomposite coatings on Ti6Al4V were attempted to fabricate by a single-step electrophoretic codeposition process for biomedical applications. The electrophoretically deposited layers with difference contents of HA, TiO₂ (anatase) and CNT nanoparticles were sintered at 800°C for densification with thickness of about 7–10 μm. A dense and crack-free coating was achieved with constituents of 85 wt% HA, 10 wt% TiO₂ and 5 wt% CNT. Open-circuit potential measurements and cyclic potentiodynamic polarization tests were used to investigate the electrochemical corrosion behavior of the coatings in vitro conditions (Hanks’ solution at 37°C). The HA/TiO₂/CNT coatings possess higher corrosion resistance than that of the Ti6Al4V substrate as reflected by nobler open circuit potential and lower corrosion current density. In addition, the surface hardness and adhesion strength of the HA/TiO₂/CNT coatings are higher than that of the monolithic HA and HA/CNT coatings without compromising their apatite forming ability. The enhanced properties were attributed to the nanostructure of the coatings with the appropriate TiO₂ and CNT contents for eliminating micro-cracks and micro-pores.     

Preparation of layered bioceramic hydroxyapatite/sodium titanate coatings on titanium substrates using a hybrid technique of alkali-heat treatment and electrochemical deposition

Bioceramic hydroxyapatite/sodium titanate coating on sandblasted titanium substrate was fabricated by a three-step process. At first, the sandblasted titanium substrate was coated with a flake-like sodium titanate layer by alkali-heat treatment. In the second step, the alkali-heat treated titanium substrate was hydrothermal treated at 180 °C for 4 h with calcium solutions. In the third step, the hydroxyapatite (HA) coating was deposited onto the hydrothermal treated layer via electrochemical deposition method. The surface topography and roughness of the coatings were determined by field emission scanning electron microscope (FESEM) and a mechanical contact profilometer, respectively. The surface compositions were evaluated by X-ray diffraction (XRD), energy-dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). The EDS, XPS, and XRD analysis confirm the presence of element Ca, Ca²⁺, and CaTiO₃ on sodium titanate layer after hydrothermal treatment with Ca(NO₃)₂ solution, respectively. FESEM micrograph shows the rod/needle-shaped crystallites are highly densely packed on the calcium-ion-containing layer with an average size of ~50 nm in diameter. The results indicate that the sodium titanate layer containing Ca²⁺ ions possesses higher ability to induce HA formation compared with the pure sodium titanate layer. It is revealed that surface composition plays an important role in the electrochemical deposition of HA. The calcium-ion-containing layer probably makes the nucleation of HA easy and effectively promotes orientated growth of HA on flake-like sodium titanate surface. The sodium titanate layer possesses a lower corrosion current density and a higher corrosion potential than sandblasted-Ti substrate. The sodium titanate layer should act as a barrier to the release of metal ions from metallic substrate to physiological solutions and thus reducing the electrochemical reaction rate.     

钛涂覆多孔羟基磷灰石涂层的制备及其生物活性

在纯钛基体表面通过电泳沉积的方法制得壳聚糖/羟基磷灰石(CS/HA)复合涂层, 然后将复合涂层烧结形成多孔HA涂层。采用SEM对多孔HA涂层的形貌进行观察, XRD分析涂层的物相组成, 粘结拉伸实验测定涂层与基体的结合强度, 1.5倍人体模拟体液(1.5SBF)浸泡测定涂层的生物活性。结果表明: 当悬浮液中CS与HA质量比为1∶1时, 制得的CS/HA复合涂层经过700℃烧结处理, 涂层中CS热分解致孔形成多孔HA涂层, 孔径在10~25 μm, 涂层与基体的结合强度可达19.5 MPa; 在1.5SBF中浸泡5天后, 多孔HA涂层表面完全碳磷灰石化, 呈现较好的生物活性。      

三维钛网表面双生物陶瓷涂层的制备及其性能

采用浸渍涂敷-烧结法首次在医用三维钛网表面制备出双生物陶瓷涂层,利用X射线衍射、场发射扫描电子显微镜对HA-BG/BG/Ti复合材料进行了微观表征,拉伸法测量了Ti基体与BG涂层的结合强度,模拟人体体液(SBF)评价复合材料的生物相容性.研究表明:该双生物陶瓷涂层的内层为生物玻璃(BG)涂层,外层为多孔结构的羟基磷灰石-生物玻璃(HA-BG)复合涂层.Ti基体被致密的BG涂层包覆,由于在BG/Ti界面发生化学反应,界面的结合强度提高,平均结合强度达27 MPa.生物相容性实验表明,HA-BG/BG/Ti复合材料表面会被一层整齐、致密的HA覆盖,具有良好的生物相容性.     

Topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite coatings on carbon fibre-reinforced poly(etheretherketone)

In the present study, topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite (HA) coatings on carbon fibre-reinforced polyetheretherketone (CF/PEEK) was performed. VPS-Ti coatings with high roughness values (Ra=28.29±3.07 m, Rz=145.35±9.88 m) were obtained. On this titanium, intermediate layer HA coatings of various thicknesses were produced. With increasing coating thickness, roughness values of the HA coatings decreased. A high increase of profile length ratio, Lr, of the VPS-Ti coatings (Lr=1.45) compared to the grit-blasted CF/PEEK substrate (Lr=1.08) was observed. Increasing the HA coating thickness resulted in a reduction of the Lr values similar to the roughness values. Fractal analysis of the obtained roughness profiles revealed that the VPS-Ti coatings showed the highest fractal dimension of D=1.34±0.02. Fractal dimension dropped to a value of 1.23–1.25 for all HA coatings. No physical deterioration of the CF/PEEK substrate was observed, indicating that substrate drying and the used VPS process parameter led to the desired coatings on the composite material. Cross-section analysis revealed a good interlocking between the titanium intermediate layer and the PEEK substrate. It is therefore assumed that this interlocking results in suitable mechanical adhesive strength. From the results obtained in this study it is concluded that VPS is a suitable method for manufacturing HA coatings on carbon fibre-reinforced PEEK implant materials.     

HA-SrCO_3-SiO_2复合涂层的制备及其生物活性

为制得在力学性能和生物活性方面都较为优异的羟基磷灰石(HA)复合涂层,首先,通过添加二元成骨微量元素化合物SrCO_3和SiO_2,以壳聚糖为造孔剂,采用电泳沉积的方法辅以高温烧结制得HA-SrCO_3-SiO_2复合涂层;然后,使用FTIR、XRD、SEM、EDS、万能材料试验机和电化学工作站对复合涂层进行测试与表征,并通过1.5倍离子浓度模拟体液的浸泡培养评价HA-SrCO3-SiO2复合涂层的生物活性。结果表明:HA-SrCO_3-SiO_2复合涂层与基体间的结合强度达28.6 MPa;在模拟体液中浸泡培养7d后,复合涂层表面完全碳磷灰石化,说明该复合涂层具有比单一掺杂成骨微量元素化合物复合涂层及纯HA涂层更为优异的生物活性。所得结论表明制得的HA-SrCO_3-SiO_2复合涂层有望开发成为新一代人工骨替代材料。     

Biomimetic apatite formation on a CoCrMo alloy by using wollastonite,bioactive glass or hydroxyapatite

A biomimetic method was used to promote a bioactive surface on a CoCrMo alloy (ASTM F75). To enhance the nucleation of apatite on the metallic substrate, wollastonite ceramics (W), bioactive glass (BG) or hydroxyapatite (HA) were used in the biomimetic method. Metallic samples were chemically treated and immersed for 7 days in SBF on a bed of bioactive material (W, BG or HA) followed by an immersion in 1.5SBF for 7 or 14 days without bioactive system.A bonelike apatite layer was formed on the surface of all the samples tested. The samples treated with wollastonite showed a higher rate of apatite formation and the morphology of the layer was closer to that of the existing bioactive systems. A higher crystallinity of the apatite layer was also observed by using wollastonite. The pH of the SBF, the Ca/P ratio and the thickness of the layer on the samples treated with wollastonite and bioactive glass increased as increasing the immersion time. The thickness of the layer on the samples treated with hydroxyapatite also increased with time, but the pH of the SBF and the Ca/P ratio changed with no a defined trend.     

Fabrication of nano-structured HA/CNT coatings on Ti6Al4V by electrophoretic deposition for biomedical applications

In order to improve the bone bioactivity and osteointegration of metallic implants, hydroxyapatite (HA) is often coated on their surface so that a real bond with the surrounding bone tissue can be formed. In the present study, cathodic electrophoretic deposition (EPD) has been attempted for depositing nanostructured HA coatings on titanium alloy Ti6Al4V followed by sintering at 800 degrees C. Nano-sized HA powder was used in the EPD process to produce dense coatings. Moreover, multiwalled carbon nanotubes (CNTs) were also used to reinforce the HA coating for enhancing its mechanical strength. The surface morphology, compositions and microstructure of the monolithic coating of HA and nanocomposite coatings of HA with different CNT contents (4 to 25%) on Ti6Al4V were investigated by scanning-electron microscopy, energy-dispersive X-ray spectroscopy and Xray diffractometry, respectively. Electrochemical corrosion behavior of the various coatings in Hanks' solution at 37 degrees C was investigated by means of open-circuit potential measurement and cyclic potentiodynamic polarization tests. Surface hardness, adhesion strength and bone bioactivity of the coatings were also studied. The HA and HA/CNT coatings had a thickness of about 10 microm, with corrosion resistance higher than that of the substrate and adhesion strength higher than that of plasma sprayed HA coating. The properties of the composite coatings were optimized by varying the CNT contents. The enhanced properties could be attributed to the use of nano-sized HA particles and CNTs. Compared with the monolithic HA coating, the CNT-reinforced HA coating markedly increased the coating hardness without deteriorating the corrosion resistance or adhesion strength.     

Anti-bacterial and cytotoxic properties of plasma sprayed silver-containing HA coatings

Silver-containing hydroxyapatite (HA) coatings have been prepared on titanium substrate by vacuum plasma spraying (VPS) method and anti-bacterial properties of the coatings were examined. Three types of bacteria stains, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, were employed in this test. The results showed that the silver-containing HA coatings exhibited significant anti-bacterial effects against the three bacteria with anti-bacterial ratios higher than 95%. The release of silver ions in the physiological environment ensured excellent anti-bacterial properties of the silver-containing HA coatings. International standard ISO 10993-12 was adopted for cytotoxicity evaluation using fibroblast cell line L929, and it was found that the cytotoxicity for the coatings ranked 0 that showed no cytotoxicity for the coatings. Hemolysis test was processed according to ASTM F 756 standard with anti-coagulated rabbit blood, and the hemolysis ratios of the coatings were below 0.4%, indicating of non-hemolysis for the coatings.     

Electrophoretic-deposited novel ternary silk fibroin/graphene oxide/hydroxyapatite nanocomposite coatings on titanium substrate for orthopedic applications

The combination of graphene oxide (GO) with robust mechanical property, silk fibroin (SF) with fascinating biological effects and hydroxyapatite (HA) with superior osteogenic activity is a competitive approach to make novel coatings for orthopedic applications. Herein, the feasibility of depositing ternary SF/GO/HA nanocomposite coatings on Ti substrate was firstly verified by exploiting electrophoretic nanotechnology, with SF being used as both a charging additive and a dispersion agent. The surface morphology, microstructure and composition, in vitro hemocompatibility and in vitro cytocompatibility of the resulting coatings were investigated by SEM, Raman, FTIR spectra and biocompatibility tests. Results demonstrated that GO, HA and SF could be co-deposited with a uniform, smooth thin-film morphology. The hemolysis rate analysis and the platelet adhesion test indicated good blood compatibility of the coatings. The human osteosarcoma MG63 cells displayed well adhesion and proliferation behaviors on the prepared coatings, with enhanced ALP activities. The present study suggested that SF/GO/HA nanocomposite coatings could be a promising candidate for the surface functionalization of biomaterials, especially as orthopedic implant coating.